Mothers with obesity at greater risk of stillbirth: Canadian study

With obesity rates rising in Canada and globally, new research suggests there is a higher risk of stillbirth in mothers with obesity. Experts say early delivery could help minimize those risks.

The study published in the Canadian Medical Association Journal (CMAJ) Monday found that maternal obesity on its own and along with other risk factors, like diabetes, high blood pressure, smoking, substance use and chronic hypertension, was associated with an increased likelihood of fetal death occurring after 20 weeks of gestation or at a birth weight of at least 500 grams.

Researchers at Dalhousie University, The Ottawa Hospital and Queen’s University analyzed data of roughly 700,000 births, out of which almost 2,000 were stillbirths, in Ontario between April 1, 2012 and December 31, 2018.

They concluded that pregnant people in the highest obesity classes II and III – with a body mass index (BMI) of more than 35.0 – have a greater overall risk of stillbirth than those with a normal BMI of 18.5–24.9. The BMI for class I obesity is in the 30.0 -34.9 range, meaning a woman of an average height weighing 200 pounds.

“What we found is that there are higher risks of stillbirth in people with obesity, especially in the higher classes and especially at term,” said Dr. Naila Ramji, a maternal-fetal medicine specialist in Fredericton, N.B., and assistant professor at Dalhousie University.

The risk of stillbirth in obese pregnancies increases with the gestational age, especially beyond 37 weeks, Ramji, who was the lead study author, told Global News.

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At around 38 weeks, the risk of stillbirth for pregnant people with obesity was roughly double to 2.5 times, compared to someone with a normal BMI and the risk was four to 4.5 times closer to 40 weeks, which is the due date, she said.

“That timing of delivery can really reduce that risk because the risk is not as high when you deliver a little bit earlier,” Ramji said.

“We think that there’s some good evidence for potentially considering delivery of individuals with class I obesity around 39 weeks and, delivering individuals with class II and class III obesity around 38 weeks to really reduce that significant jump in stillbirth risk that happens after that time in those populations.”

There is already precedence in Canada of early induction of labour between 38 to 39 weeks for women with Type I and Type II diabetes or for those who have a high blood pressure because they are also at a higher risk of stillbirth than the average pregnant person, she said.

The same approach should be considered for people with obesity, Ramji said, where the labour can be induced as long as there are no contradictions.

It could also be a planned cesarean delivery if it is not safe to deliver vaginally due to some other pregnancy issues.

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One in four Canadians are living with obesity, according to Obesity Canada. As of 2022, 4 million women and 4.4 million men were living with obesity in the country, data from a global analysis published in the Lancet journal showed on Friday.

Between 1990 and 2022, obesity rates among adults have more than doubled worldwide and increased four times in children and adolescents.

The authors of the Lancet study believe the shift in the onset of obesity in young people over the three decades could be because of access to commercial and processed foods in school-aged children.

People with obesity are at higher risk of developing pregnancy complications and that can lead to stillbirths, Ramji said.

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While the CMAJ study did not specifically explore the reasons behind the association between maternal obesity and stillbirths, Ramji said factors like inflammation and alterations in metabolism could be playing a role here.

She said besides the timing of delivery, obese pregnancies should be monitored more closely for any complications. As with all pregnancies, Ramji advised against smoking, substance use and urged good nutrition and daily activity to help reduce the risk of stillbirth.

In a related article also published Monday, Dr. Naomi Cahill, CMAJ editor and registered dietitian, said: “Pregnant people living with obesity should receive respectful prenatal care, free from stigma, that realizes the goals of both health-care providers and patients to ensure positive maternal and fetal outcomes.”

— With files from Global News’ Katie Dangerfield